U.S. Pat. No. 4,766,405 describes a fuel injector that includes a valve-closure member which is joined to a valve needle and cooperates with a valve-seat surface formed on a valve-seat member to form a sealing seat. For the electromagnetic actuation of the fuel injector, a magnetic coil is provided which cooperates with an armature that is joined to the valve needle by force-locking. An additional mass having a cylindrical form is provided around the armature and the valve needle, the mass being connected to the armature via an elastomeric layer.
The disadvantage with this is particularly the costly design that includes an additional component. In addition, the large surfaced elastomer ring is disadvantageous for the pattern of the magnetic field and hinders the closing of the field lines, and thus the achievement of high attractive forces during the opening movement of the fuel injector.
U.S. Pat. No. 4,766,405 describes another embodiment of a fuel injector in which, for damping and debouncing, an additional cylindrical mass is provided around the armature and the valve needle, which is moveably braced and held in its position by two clastomeric rings. When the valve needle strikes the sealing seat, this second mass can move relative to the armature and the valve needle and prevent bouncing of the valve needle.
The disadvantage of this described specific embodiment is the additional cost and space requirement. Also, the armature itself is not decoupled, so that its momentum increases the bouncing tendency of the valve needle.
U.S. Pat. No. 5,299,776 describes a fuel injector having a valve needle and an armature, where the armature is movably guided on the valve needle. The armature movement in the lift direction of the valve needle is limited by a first stop and its movement counter to the lift direction by a second stop. Within certain limits, the axial play of the armature, defined by the two stops, leads to a decoupling of the inert mass of the valve needle on the one hand, and the inert mass of the armature on the other hand. This counteracts to some extent a bouncing back of the valve needle from the valve-seat surface upon closing of the fuel injector. However, since the axial position of the armature relative to the valve needle is totally undefined by the free movement of the armature relative to the valve needle, bounces are avoided only to a limited extent. In particular, in the design of the fuel injector of U.S. Pat. No. 5,299,776 it is not avoided that the armature strikes the stop facing the valve-closure member during the closing movement of the fuel injector, thereby rapidly transmitting its momentum to the valve needle. This sudden transfer of linear momentum may cause additional bounces of the valve-closure member.
Furthermore, it is known in practice to fasten the armature, which is movably positioned on the valve needle, by using an elastomeric ring so that it is movably clamped in its position. For this purpose, the armature is held between two stops, an elastomeric ring being situated between the armature and lower stop. With this arrangement, however, the problem arises that a borehole through the armature is necessary for the supply of fuel to the valve-sealing seat. The bore through the armature is implemented close to the valve needle, so that it may occur that the elastomeric ring covers the bore.